Help needed with gift for boyfriend

I'm familiar with pokémon and used to collect pokémon cards (none with significant value) when I was a kid, but I'm not a super fan who knows a whole lot about it. My boyfriend, on the other hand, is.

He doesn't have many pokémon cards at the moment because he's only recently become re-interested in it and started recollecting them. He doesn't have any major ones, he's just opened a few packs. But he's always talking about it and how much he wants to rebuild his collection. (He had a tonne when he was a kid that are now worth thousands but sold them all for 100 to make a quick buck when he was younger).

His birthday is coming up. I know he's very interested in the 151 booster bundles, and I believe he's interested in the Prismatic Evolutions trainer boxes and those sets that have a few already opened cool ones with them alone with some packs. But I'm not completely sure what to get him. My budget is about 250-300. I'm also thinking about getting a single card (preferably an old Mew card since that's his favourite Pokémon), and maybe a binder. I'd appreciate any suggestions, like what's best for value, where to get them, etc.

Any help it's greatly appreciated, all I want is for him to be happy, especially on his birthday.